1. Field of the Invention
The present invention relates to an initiator assembly used in various kinds of gas generators such as a gas generator for an air bag, a gas generator for a seatbelt pretensioner, and a gas generator for a curtain air bag, which are safety systems of motor vehicles, and more particularly, to an initiator assembly in which an electric type initiator adapted to be actuated by an electrical signal and a metallic collar surrounding at least part of the electric type initiator are integrated with resin, a gas generator using this assembly, and a combined structure of a metallic collar and a resin in the initiator assembly.
2. Description of Related Art
An initiator assembly includes an electric type initiator adapted to be actuated by an electrical signal from a collision detecting system, and it is mounted, interposing a metallic collar or the like, to various safety devices for a motor vehicle, such as a gas generator for an air bag, a gas generator for a seatbelt pretensioner, a gas generator for a curtain air bag, and the like. Since the initiator assembly has to actuate these safety devices, reliable actuation of the initiator assembly is essential in order to actuate a gas generator unfailingly.
Also, generally in the initiator assembly, a priming included in an electric type initiator is ignited and burnt, so that it is necessary for the priming to avoid moisture absorption in order to securely actuate the initiator assembly. Furthermore, since the initiator assembly is mounted to a gas generator, it is necessary to securely seal a mounting portion of the initiator assembly to the gas generator or to seal between respective constituent elements in the initiator assembly itself in order to prevent moisture absorption of explosives as a gas generating agent charged in the gas generator. Further, the above-described operation of the initiator assembly must be not only secured, but also facilitate a manufacture of an initiator assembly itself or an assembling of the initiator assembly to a gas generator.
A conventional initiator assembly is disclosed in, for example, JP-A 11-321541. An initiating device assembly (an initiator assembly) disclosed in this publication is obtained by integrating an initiating device and a collar assembly with an injection-molded insulating material, which reduces a size of the injection-molded portion and that combines the initiating device assembly and an inflator apparatus properly and easily.
However, in the initiator assembly disclosed in this publication, nothing is considered concerning improvement of the operation reliability in the initiator assembly itself and a secure actuation in the gas generator.
Accordingly, in the conventional initiator assemblies, there is still a room to be improved in view of realizing a sufficient operation reliability and facilitating a manufacturing.
Under these circumstances, the present invention provides an initiator assembly in which a combined structure of a metallic collar and an electric type initiator is reliable to block entering of a moisture into the gas generator, and an operation reliability is secured, not increasing manufacturing steps or manufacturing cost.
The above-described problem is solved by an initiator assembly of the present invention provided with features described below.
That is, the present invention provides the initiator assembly in which an electric type initiator and a metallic collar surrounding at least part of the electric type initiator are integrated with a resin, wherein at least one of an annular protrusion and a cylindrical protrusion provided in a direction of surrounding the electric type initiator is formed on the metallic collar, and the protrusion is covered with the resin.
The electric type initiator is actuated on the basis of an actuation signal to generate a flame for actuating a gas generator, and it includes at least a single electroconductive pin, means for converting electrical energy received by the electroconductive pin to thermal energy (for example, a bridge wire), and a priming which is ignited by the converted thermal energy to be burnt. Also, the metallic collar is for fixing the electric type initiator to the gas generator and it has at least one or more protrusions.
The protrusion is formed in an annular shape and/or a cylindrical shape to surround the electric type initiator, and it is formed on the metallic collar. As this protrusion, one or plural annular projections can be provided, or one or plural cylindrical projections can be provided or both an annular protrusion and a cylindrical protrusion can be provided. For example, when the metallic collar has an inner hole which the electroconductive pin of the electric type initiator passes through, the protrusion can be provided at a portion where the inner hole is formed. Also, the protrusion can be formed at an end surface of the metallic collar in a cylindrical shape to surround a periphery of the electric type initiator. In particular, the protrusion which is formed cylindrically is desirable, because a surface area of the protrusion can be obtained largely and a contacting area with resin can be made large enough.
The protrusion is covered with a resin integrating the electric type initiator and the metallic collar, and preferably, the protrusion is held in the thickness direction by the resin. By holding the protrusion with resin, the metallic collar and the resin can be combined more securely, so that a gap to allow moisture to pass through cannot be made between the both. In order to interpose the protrusion the resin, preferably, molding-shrinkage or post-shrinkage of the resin is utilized. Accordingly, it is preferable that the resin integrating the electric type initiator and the metallic collar is injection-molded between the both members. It is also preferable that the resin is injected to cover the protrusion in the injection-molding. The resin desirably molding-shrinks or post-shrinks by the injection-molding so that the resin can hold the protrusion.
As described above, in the initiator assembly of the present invention, the protrusion is provided at the metallic collar, so that the metallic collar and the resin can be combined securely by utilizing the molding-shrinkage or the post-shrinkage of resin without causing any difficulty in manufacturing.
Incidentally, taking account of interposing the protrusion by a molding-shrinkage or a post-shrinkage of a resin, preferably, the protrusion is made thicker, but not to such an extent that a structure of the initiator assembly is disturbed. For this reason, it is preferable that the thickness of the protrusion is decided in view of a molding-shrinkage rate of resin to be used.
In the present invention, a preferable resin which integrates the electric type initiator and the metallic collar has the molding-shrinkage rate of 1% or less, more preferably between 0.1 and 0.8%. Even a resin which becomes solidified after being injection-molded can be used in the initiator assembly of the present invention because any resin molding-shrinks to some extent. However, a resin with such a large molding-shrinkage that a molding-shrinkage rate exceeds 1% is undesirable because it is deformed, warped or obtains a shrink mark after solidification, and consequently, a gap may be formed between the electrical type initiator and the resin or between the metallic collar and the resin. When the molding-shrinkage rate is not less than 0.1%, the protrusion can be held securely by the molding-shrinkage of resin, which is preferable.
Incidentally, a resin containing inorganic charging material such as glass fiber, inorganic filler or the like is known that molding-shrinkage rates in a flowing direction (MD) of injection-molded resin and in a direction (TD) perpendicular thereto are different from each other due to the orientation of the organic filling material. Therefore, in case that such a resin is used, a resin having such molding-shrinkage rates (in the flowing direction and the perpendicular direction) that no undesirable gap occurs at least between the electric type initiator and the resin, between the metallic collar and the resin, or the like is used.
Also, the resin containing inorganic charging material has the molding-shrinkage rate in the perpendicular direction larger than in the flowing direction, and preferably, the protrusion is formed to be thicker in the perpendicular direction of the resin than in the flowing direction of the resin. With this, the protrusion is held more securely by the molded-shrunk resin while suppressing the shrinkage coefficient in the flowing direction of resin.
Accordingly, when the protrusion is formed in a cylindrical shape to surround the initiator assembly and the protrusion is held by the molded-shrunk resin in the thickness direction thereof, it is preferable that the resin is injected to flow in the axial direction of the cylindrical protrusion.
Also, as a resin used in this invention, a thermosetting resin can be used, but a thermoplastic resin is preferably used in view of injection-molding, and a resin containing glass fiber or other inorganic charging material is more preferably used. In the resin, a coefficient of water absorption after being submerged for 24 hours at 23xc2x0 C. (the same will apply thereinafter) is preferably 0.005 to 0.5% is used, more preferably 0.005 to 0.3%, and a tensile strength is preferably 70 to 250 MPa, more preferably 100 to 250 MPa. Further, it is desirable to use a resin in which a coefficient of linear expansion is not more than 8xc3x9710xe2x88x925/xc2x0 C., the tensile strength is not less than 100 MPa and a dielectric breakdown voltage is not less than 10 MV/m. In particular, the tensile strength is preferably not less than 170 MPa but not more than 250 MPa. Accordingly, the tensile strength is preferably not less than 100 MPa but not more than 250 MPa, most preferably, not less than 170 MPa but not more than 250 MPa.
Examples of such a resin include nylon 612, polyacrylate, polybutylene telephtalate, polyphenylene sulfade or liquid crystal polymer. These resins may contain inorganic charging material such as glass fiber, glass filler, or mineral. In particular, it is preferable that glass fiber of 20 to 80 weight % is contained in polybutylene telephtalate, glass fiber of 20 to 80 weight % is contained in polyphenylene sulfade and mineral of 20 to 80 weight % is contained in liquid crystal polymer. Particularly, in case of using glass reinforced resin containing glass fiber, the orientation of the glass fiber is desirably adjusted to be along the extending direction of an electroconductive pin inserted into the resin. This is because the molding-shrinkage rate of the resin in the thickness direction of the electroconductive pin becomes larger enough to securely block permeation of moisture between the pin and the resin. Also, a percent content of inorganic charging material in each resin material is more preferably 20 to 50 weight %.
By holding the protrusion with the above-described molding-shrinking resin after being injection-molded, moisture does not penetrate the resin to reach the priming, so that deterioration due to moisture absorption in a priming can be avoided as much as possible. That is, when the electric type initiator and the metallic collar are integrated with each other using such a resin, such an initiator assembly can be obtained that can exhibit an original operation after being left in a motor vehicle or the like for a long term. In particular, polyphenylene sulfade or liquid crystal containing filling material preferably is used, because high productivity and low cost can be achieved by injection-molding.
Also, in the initiator assembly of the present invention, it is preferable that a rotation-preventing means which prevents rotation of the resin and the metallic collar is provided in order to further securely combine the resin and the metallic collar. An example of such a rotation-preventing means can be formed by providing an concavo-convex portion on the metallic collar in a contacting surface between the metal collar and the resin to make the resin engaged with the concavo-convex portion. The concavo-convex portion can also be formed on the above protrusion, and when the concavo-convex portion is formed on the protrusion in the surface held by the resin, the concavo-convex portion and the resin can be securely engaged with each other to prevent rotation between the resin and the metallic collar.
However, when the concavo-convex portion is formed on the metallic collar as the rotation-preventing means, it is preferable that the resin engaged with the concavo-convex portion is formed not to be damaged by a pressure due to actuation of the electric type initiator. For example, in order to eliminate a possibility such that the concavo-convex portion causes a resin cracking, no concavo-convex portion is preferably formed on the metallic collar in a portion or a surface which supports the electric type initiator against a pressure generated at a time of actuation of the electric type initiator. Accordingly, in case of forming the rotation-preventing means comprising an concavo-convex portion on the protrusion, the rotation-preventing means is preferably formed on a cylindrical protrusion extending in the axial direction of the initiator assembly.
Also, if the inner hole of the metallic collar in which the electroconductive pin of the electric type initiator passes through is formed to have a smaller inner diameter portion than at least an outer diameter of the electric type initiator, the electric type initiator never passes through the inner hole to fall off due to that the resin melts by heat at a time of actuation of the electric type initiator. For example, a projection extending radially and inwardly is formed on a wall surface in which the inner hole is formed and also, the inner hole may be formed in an oval shape, a rectangular shape, various polygonal shapes or shapes similar thereto. In the metallic collar thus formed, the electric type initiator is supported by the inner hole in part having a smaller inner diameter, and thereby, the electric type initiator does never pass through the inner hole. Furthermore, the inner hole is formed in any shape except for a circular shape, for example, an oval shape (see FIG. 5), a polygonal shape (see FIG. 6), or the like, which is advantageous to prevent rotation between the resin and the collar. Accordingly, it is desirable to form the inner hole in a shape that can block rotation between the resin and the collar.
Further, in the above-described initiator assembly, the metallic collar in a portion for receiving a connector is not covered with the resin, exposing this portion of the metallic collar. Thereby, there can be eliminated a possibility such that the connector received at this portion may be dislocated due to reaction at a time of actuation of the initiator assembly.
Also, in the initiator assembly, since the resin can be fixed to the metallic collar at the above-described protrusion, an excess resin required for fixing the both can be decreased to reduce manufacturing cost.
In the above-described initiator assembly, not only that a single electric type initiator is provided in a single metallic collar, but also that two electric type initiators may be provided in a single metallic collar. Even when two electric type initiators are provided in a single metallic collar, the collar and the initiators can be integrated with resin, and the resin and the metallic collar can be combined securely by providing the above-described protrusion in the collar.
The above-described initiator assembly can be accommodated in a housing having a gas discharging port together with, for example, a gas generating agent to be burnt and/or inflated at actuation for generating an operating gas, thereby forming a gas generator for an air bag of the present invention.
In the gas generator of the present invention using the above-described initiator assembly, the metallic collar and the resin is combined securely and moisture cannot penetrate from this portion. For this reason, moisture absorption of the gas generating agent or the like can be avoided, and operation reliability of the gas generator can be guaranteed even after a long-term service, and also, an original operation performance can be obtained.
Such a gas generator may include a single or at least two combustion chambers accommodating a gas generating agent in a housing or may be filled with a pressurized medium in addition to the gas generating agent to be burnt to generate an operating gas. Also, the gas generator is not used only for a gas generator used for an air bag, but also for the one used for a seatbelt pretensioner or the one used for a curtain air bag.
According to the present invention, moisture can effectively be prevented from penetrating the inside of an igniter without causing increase in manufacturing cost of an initiator assembly. Further, in a gas generator using this initiator assembly, since moisture cannot penetrate the inside of the initiator assembly, moisture-absorption and deterioration of a gas generating agent (a priming) can effectively be prevented, so that a gas generator which can maintain an original performance even after a long-term service can be obtained.